#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/ktime.h>
#include <linux/sched.h>

#define ORIG_FUNC_NAME "_do_fork"

/* per-instance private data */
struct my_data {
  ktime_t entry_stamp;
};


/* Here we use the entry_handler to timestamp function entry */
static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
{
  struct my_data *data;

  if (!current->mm)
    return 1; /* Skip kernel threads */

  data = (struct my_data *)ri->data;
  data->entry_stamp = ktime_get();

  return 0;
}
NOKPROBE_SYMBOL(entry_handler);

/*
 * Return-probe handler: Log the return value and duration. Duration may turn
 * out to be zero consistently, depending upon the granularity of time
 * accounting on the platform.
 */
static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
{
  unsigned long retval = regs_return_value(regs);
  struct my_data *data = (struct my_data*)ri->data;
  s64 delta;
  ktime_t now;

  now = ktime_get();
  delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));
  pr_info("%s returned %lu and took %lld ns to execute\n",
      ORIG_FUNC_NAME, retval, (long long)delta);
  return 0;
}
NOKPROBE_SYMBOL(ret_handler);

static struct kretprobe my_kretprobe = {
  .handler = ret_handler,
  .entry_handler = entry_handler,
  .data_size = sizeof(struct my_data),
  /* Probe up to 20 instances concurrently. */
  .maxactive = 20,
};

static int __init kretprobe_init(void)
{
  int ret;

  my_kretprobe.kp.symbol_name = ORIG_FUNC_NAME;

  ret = register_kretprobe(&my_kretprobe);
  if (ret < 0) {
    pr_err("register_kretprobe failed, returned %d\n", ret);
    return ret;
  }

  pr_info("Planted return probe at %s: %p\n",
      my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr);

  return 0;
}


static void __exit kretprobe_exit(void)
{
  
  unregister_kretprobe(&my_kretprobe);
  pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr);

  /* nmissed > 0 suggests that maxactive was set too low. */
  pr_info("Missed probing %d instances of %s\n",
    my_kretprobe.nmissed, my_kretprobe.kp.symbol_name);

}

module_init(kretprobe_init);
module_exit(kretprobe_exit);


MODULE_LICENSE("GPL");

